Toyota Celica 2005 Repair Manual page 265

DI−66
CIRCUIT DESCRIPTION
Refer to DTC P0130 on page DI−112.
HINT:
The ECM provides a pulse width modulated control circuit to adjust current through the heater. The heated
oxygen sensor heater circuit uses a relay on the B+ side of the circuit.
Reference (Bank 1 Sensor 1 System Drawing):
EFI Fuse
From
Battery
From
Terminal 6 of
Ignition Switch
DTC No.
P0031 Heated current is 0.25 A or less when heater operates with
P0037 B+ greater than 11.5 V (1 trip detection logic)
P0032 Heated current exceeds 3.5 A when heater operates
P0038 (1 trip detection logic)
HINT:
Sensor 1 is the sensor closer to the engine body.
S
Sensor 2 is the sensor farther away from the engine body.
S
MONITOR DESCRIPTION
The sending portion of the heated oxygen sensor has a zirconia element that is used to detect oxygen con-
centration in the exhaust. If the zirconia element is at the proper temperature and the difference of the oxy-
gen concentration between the inside and outside surface of the sensor is large, the zirconia element will
generate voltage signals. In order to increase the oxygen concentration detecting capacity in the zirconia
element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sen-
sor. When current in the sensor is out of the standard operating range, the ECM interprets this as a fault in
the heated oxygen sensor and sets a DTC.
Example:
The ECM will set a high current DTC if the current in the sensor is more than 2 A when the heater is OFF.
Similarly, the ECM will set a low current DTC if the current is less than 0.25 A when the heater is ON.
2005 CELICA (RM1131U)
DIAGNOSTICS
EFI Relay
Heated Oxygen Sensor
Ground Ground
DTC Detection Condition
− ENGINE (1ZZ−FE)
Heater
Sensor
S Open or short in heater circuit of heated oxygen sensor
S Heated oxygen sensor heater
S EFI relay
S ECM
264
ECM
HT1A
OX1A
Duty
Control
Trouble Area
A21410